JPH0474830B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a battery using a non-aqueous electrolyte, and more specifically, it suppresses an increase in internal impedance during high-temperature storage of the battery, and improves the use of the battery. This greatly expands the temperature range.

Conventional configurations and their problems Conventionally, when batteries are stored at high temperatures, especially at temperatures above 45°C, the capacity decreases and the internal impedance increases due to self-depletion of the active material, chemical changes in the materials used, etc. There were problems such as not being able to draw electric current.

Among various battery systems, non-aqueous electrolyte batteries have excellent high-temperature storage performance. Therefore, its uses are rapidly expanding in recent years. However, this non-aqueous electrolyte battery also has its limitations and is not completely satisfactory for use in high-temperature atmospheres.

For example, a battery uses lithium as the negative electrode active material, a non-aqueous electrolyte in which lithium borofluoride is dissolved in γ-butyrolactone as the electrolyte, carbon fluoride as the positive electrode active material, and titanium as the positive electrode current collector. Due to its operability in a wide range of temperatures, excellent storage stability, and reliability, it is used in large quantities as a power source for electronic watches, cameras, communication devices, and various backup devices, and is expected to grow dramatically in the future.

At the same time, there is a demand for batteries to be usable under any conditions around the world. However, in conventional non-aqueous electrolyte batteries, when the batteries are stored in high temperatures, especially in an atmosphere of 70°C or higher, the internal impedance gradually increases.
There was a problem in that the operating voltage decreased when using batteries.

The cause of this is that the current collector is halogen, or fluorine ion, originating from lithium borofluoride, a halogen compound used in the electrolyte of the non-aqueous electrolyte, or from carbon fluoride used in the positive electrode active material. It was speculated that titanium reacts with titanium at high temperatures to form titanium fluoride, increasing internal impedance.

As an improvement measure, the titanium current collector is coated with carbon paint to form a carbon film, or the titanium current collector is coated with palladium.
Methods of plating precious metals such as silver and gold have been proposed.

However, these methods are not adopted from an industrial practical standpoint because there is no suitable carbon paint with specific electrolyte resistance and adhesion, and plating precious metals is extremely expensive. has not been reached.

OBJECTS OF THE INVENTION The present invention solves the problems of the conventional example, and solves the increase in internal impedance during high-temperature storage of a non-aqueous electrolyte battery that uses a halogen compound in at least one of the positive electrode active material and the electrolyte. The purpose is to prevent this and improve high-temperature storage properties.

Structure of the Invention In order to achieve the above object, the present invention includes a negative electrode using a light metal such as lithium as an active material, a positive electrode, and a non-aqueous electrolyte, and at least one of the positive electrode active material and the electrolyte contains a halogen compound. For example, in batteries using carbon fluoride or lithium borofluoride,
It is characterized by using titanium having an oxide film with a thickness of 0.01 to 0.2 microns on the surface as the current collector of the positive electrode. With such a configuration, titanium and fluorine ions can be prevented from reacting at high temperatures to produce titanium fluoride, and an increase in internal impedance of the battery during storage at high temperatures can be prevented.

FIG. 1 is a longitudinal sectional view showing a typical structure of the battery of the present invention. In the figure, 1 is a positive electrode, which is a current collector 1' made of expanded titanium metal and coated with a positive electrode mixture. The positive electrode mixture is prepared by kneading carbon fluoride as an active material with acetylene black as a conductive agent and an aqueous dispersion of ethylene tetrafluoride as a binder.
2 is a lithium sheet which is a negative electrode active material, and an expanded metal 2' made of nickel as a current collector is press-fitted into one side of the lithium sheet. It is welded to the inner bottom of the battery case 3.

The above-mentioned positive electrode 1 and negative electrode 2 are entirely wound in a spiral shape with a separator 4 made of a nonwoven polypropylene fabric interposed therebetween, and are housed in a battery case 3. 5 is a positive electrode lead made of titanium,
One end is welded and integrated with the titanium current collector 1' of the positive electrode 1, and the other end is a titanium washer fixed to the center of the lower surface of the sealing plate 6 made of polypropylene with an aluminum rivet 7. It is welded to 8. A titanium washer 9 is fixed to the upper surface of the sealing plate 6 by a caulked portion of a rivet 7, and a cap 10 forming a positive electrode terminal is welded to the periphery of the titanium washer so as to surround the rivet. 11 is a bottom insulating ring, and 12 is an exterior resin tube. In addition, the electrolyte contains γ-
Lithium borofluoride dissolved in butyrolactone in an amount of 1 mol/mole was used as an electrolyte.

The internal resistance of this battery is approximately 0.4Ω immediately after assembly.
It is. Furthermore, even after 5 years of storage at room temperature, the internal resistance is 0.6Ω, which is about 1.5 times that immediately after assembly, so there is no practical problem with storage at room temperature.
However, when stored at a high temperature of 70°C or higher, the internal resistance increases significantly; for example, after being stored at 70°C for one month, the internal resistance increases by 2 to 10 times to about 0.8 to 4Ω.

After disassembling and analyzing a battery whose internal resistance had risen to approximately 4Ω, it was discovered that the cause was in the positive electrode. As a result of further observation of this positive electrode,
It became clear that the resistance between the mixture layer and the current collector made of expanded titanium metal increased.

Further, as a result of observing the surface of the titanium current collector of the battery with increased internal resistance using an electron microscope and an X-ray microanalyzer, it became clear that a fluoride layer was formed on the surface of the current collector.
As a result, as expected by the inventor, it was confirmed that the internal resistance increased due to the formation of fluoride on the surface of the current collector.

In this case, the titanium used for the current collector is
It is thought that the fluoride layer was formed by reacting with free fluorine or fluorine ions from carbon fluoride, which is the positive electrode active material, or lithium borofluoride, which is the solute.

Although titanium is a material with excellent corrosion resistance, it has been known for some time that it is relatively susceptible to halogens. Therefore, if the active material or electrolyte contains a halogen compound and titanium is used as a current collector, the same phenomenon as described above is thought to occur, and especially when the battery is stored at high temperatures, the formation of halides. It is thought that the speed will be extremely accelerated.

In that sense, it is not necessarily suitable as a current collector when the positive electrode active material or electrolyte contains halogen compounds, but other common metals have no corrosion resistance and will corrode even at room temperature, excluding precious metals. However, it is completely unusable, and titanium has no choice but to be used as a current collector.

Therefore, in order to prevent the internal resistance of the battery from increasing during high-temperature storage, measures should be taken to prevent fluoride from forming on the titanium surface during high-temperature storage.

The present inventors focused on this point, and by pre-treating the titanium current collector to form a controlled oxide film on the surface, the halogen-free surface of the titanium current collector can be removed even when the battery is stored at high temperatures. This was successful in preventing the formation of chemical compounds.

The present invention will be explained in detail below using specific examples.

Description of Examples (Example 1) Generally, the surface of titanium is covered with a naturally generated oxide film, and the thickness thereof is said to be 5 to 70 Å.

When titanium is heated in air, which is an oxygen-containing atmosphere, this oxide film grows. At the same time, when the thickness of the oxide film becomes several hundred angstroms, a coloring phenomenon occurs due to the interference effect of light.

Generally, it is said that the heating temperature, the thickness of the oxide film, and the coloring of the surface have a relationship as shown in FIG.

In the battery shown in Fig. 1, the expanded titanium metal that is the positive electrode current collector is heated at 1) 100°C, 2) 150°C, 3) 200°C,
4) 250℃, 5) 300℃, 6) 350℃, 7) 400℃,
Heat treatment was performed for 30 minutes at each temperature of 8) 450°C, 9) 500°C, 10) 600°C, and 11) 700°C. At this time, an oxide film was formed on the surface of the expanded titanium metal, giving it different colors. For example, 1) and 2) were almost the same as the silvery white before treatment, and 3) was silvery white, but a slight pale yellow coloration was observed in some parts. 4) and 5) had a pale yellow to yellow or golden color. Samples 6) and 7) had a golden color, and sample 8) had a blue color with some parts showing a golden color. Further, 9) had a blue color, 10) had a bluish-purple color, and 11) had a purple to gray color. These 1) to 11) 11 types of titanium current collectors are used as positive electrodes coated with a positive electrode mixture, and the rest is the same battery as the battery with the configuration shown in Figure 1 detailed in the configuration of the invention. It was created.

(Example 2) In the battery shown in Fig. 1, the expanded titanium metal that is the positive electrode current collector was chemically polished by a known appropriate method before making the positive electrode, and then polished in 12) 0.1 wt% dilute sulfuric acid. Boil for 24 hours.
13) Boil in 0.2wt% diluted hydrochloric acid for 24 hours. 14)
Boiled in 30wt% nitric acid for 24 hours.

Even when oxidized by chemical oxidation methods such as immersion in the above-mentioned inorganic acids or leaving in the atmosphere,
An oxide film was formed on the surface of the expanded titanium metal, and at the same time it took on a color. For example, 12) was colored blue-purple, 13) was colored golden yellow, and 14) was colored pale yellow. The battery shown in FIG. 1 was made using these titanium current collectors.

(Example 3) In the battery shown in Figure 1, the expanded metal of titanium as the positive electrode current collector was placed in an electrolytic solution prepared by adding phosphoric acid to a dextrin aqueous solution with a concentration of 1wt% before making the positive electrode, and stainless steel was used as the negative electrode. using a titanium expanded metal as the positive electrode,
The surface of the titanium was oxidized using the so-called anodic oxidation method, which involves passing a direct current at a voltage of 70V.

Even with this method, yellow coloration was observed due to the formation of an oxide film. The battery shown in FIG. 1 was prepared using this expanded titanium metal as a current collector.

After each of the batteries described in the above examples was stored in an atmosphere at 70°C for one month, the internal impedance of the batteries was measured using an alternating current method at 1 Kz and 10 mA, and the effect of the oxide film on the titanium surface was investigated. .

Figure 3 shows the internal impedance values of a battery using expanded titanium metal heat-treated at various temperatures as the current collector as described in Example 1, immediately after assembly (A) and after storage at 70°C for one month (B). show. All values indicate average values for 10 batteries. As is clear from Figure 3, the expanded titanium metal is heated to 200°C or higher, preferably 250 to 700°C.
When heat treated at 70°C, there is little increase in internal impedance after storage at 70°C for one month. In other words, 200℃～
When treated at 250°C, the expanded titanium was colored pale yellow and an oxide film with a thickness of about 0.01 μm or more was formed on the titanium surface, and the high-temperature storage properties were good. However, for those treated at a temperature higher than 700°C, the characteristics after being stored at 70°C for one month are almost the same as the initial ones, and the initial internal impedance before storage is as high as about 1.5Ω, which is undesirable.
As a result of being heated to a high temperature of 700°C, it takes on a gray color and the thickness of the oxide film is about 0.2 to 0.3μ, which acts as a surface protection film and also a passive film, increasing the internal impedance of the battery. Conceivable. Furthermore, if the oxide film becomes gray, problems such as peeling may occur.

Therefore, for high-temperature storage, the thickness of the oxide film on the surface of titanium is considered to be 0.01 to 0.2 μm. Expressed in another way, it can be said that an oxide film having an interference color between pale yellow and purple shown in FIG. 2 is appropriate.

In Example 1, the expanded titanium metal was heat treated at each temperature for 30 minutes, but if the heat treatment time is changed, the thickness of the oxide film produced will vary even at the same temperature. For example, in the example, it was slightly yellowish in some parts.
Even in the treatment at 200°C, if the treatment is carried out for 180 minutes, a considerable portion becomes pale yellow, which is the same as in Example 1.
The result is close to that of heat treatment at 250℃.

Therefore, what is more important in this case is the thickness of the film formed on the titanium surface than the processing temperature.
Alternatively, more importance should be placed on the degree of coloring.

FIG. 4 shows the battery of FIG. 1 using the expanded titanium metal obtained by the methods of Examples 2 and 3.
Internal impedance C after storage at 70℃ for 1 month
is shown in comparison with that D immediately after battery assembly. In this case as well, the internal impedance of the untreated material increased significantly after being stored at 70°C for one month.
Alternatively, for those on which an oxide film was formed by anodic oxidation, there was only a slight increase in internal impedance even after storage at 70°C for one month.

This improves high-temperature storage by forming a thick oxide film with a pale yellow to bluish-purple color on the surface of the expanded titanium metal.

As described in the above examples, titanium was surface-oxidized in advance by various methods and used as a current collector for the positive electrode, and as a result, the high-temperature storage characteristics of the battery were significantly improved. This is due to the formation of an oxide film that is slightly thicker and more stable than the oxide film that naturally forms on the surface of titanium, resulting in corrosion resistance against halogens, which are components of the positive electrode active material or electrolyte within the battery. This is thought to be because the formation of halides on the surface of the titanium current collector, which was the cause of the increase in internal impedance during high-temperature storage, was suppressed.

After disassembling the battery after being stored at 70°C for one month, we measured the amount of fluorine on the surface of the positive electrode current collector using an X-ray microanalyzer.As a result, we found that the surface of the titanium current collector had a pale yellow to purple color in advance. The one that was oxidized as shown in Figure 1 was 900 pulses/10 seconds, while the one that used an untreated titanium current collector was 5,300 pulses/10 seconds, although it did form an oxide film. This is supported by the fact that 6 times as much fluorine was detected.

In the examples, only the case where carbon fluoride was used as the positive electrode active material and lithium borofluoride was used as the solute of the electrolyte was described. It is obvious that the present invention can be applied to batteries using halogen compounds.

For example, the present invention can be achieved even when a halogen compound is present in only one of the positive electrode active material and the electrolyte shown in the above examples. In addition, in the case of batteries using other active materials, for example, when manganese dioxide is used as the positive electrode active material and lithium perchlorate is used as the electrolyte,
Or LiBF ₄ , LiAC ₄ , AC as electrolyte
Of course, this also includes cases where halogen compounds such as ₃ and LiAsF ₆ are used alone or in combination. Furthermore, it will be understood that cases in which thionyl chloride (SOC ₂ ) is used as the positive electrode active material are also included.

Effects of the Invention As described above, the present invention provides a battery in which at least one of the positive electrode active material or the electrolyte in the non-aqueous electrolyte contains a halogen compound and uses titanium as the positive electrode current collector.
By forming and using an oxide film with a thickness of 0.2μ or a pale yellow to purple color, the high temperature storage characteristics of the battery are significantly improved and the temperature range in which the battery can be used is expanded.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing a typical structure of the battery according to the present invention, FIG. 2 is a diagram showing the relationship between the heating temperature of titanium, which is the positive electrode current collector, and the thickness and coloration of the oxide film. is the heat treatment temperature of titanium and 1 at 70℃ for a battery using treated titanium as the positive electrode current collector.
FIG. 4 is a diagram showing changes in internal impedance before and after storage for one month at 70°C of a battery with an oxide film formed on the titanium surface according to another embodiment of the present invention. be. 1... Positive electrode, 1'... Titanium positive electrode current collector, 2
... Negative electrode, 2'... Negative electrode current collector, 3... Battery case, 4... Separator.

Claims (1)

[Scope of Claims] 1. A battery comprising a negative electrode using a light metal as an active material, a positive electrode, and a nonaqueous electrolyte, and using a halogen compound as at least one of the active material and the electrolyte of the positive electrode, The current collector of the positive electrode has a thickness of 0.01 mm on the surface.
A battery made of titanium with an oxide film of ~0.2 microns. 2. The battery according to claim 1, wherein the oxide film on the titanium surface is formed by heat treating titanium at 250 to 700°C in an oxygen-containing atmosphere. 3. The battery according to claim 1, wherein the oxide film on the titanium surface is formed by a chemical oxidation method in which titanium is immersed in an inorganic acid or left in an inorganic acid atmosphere. 4. The battery according to claim 1, wherein the oxide film on the titanium surface is formed by an anodic oxidation method in which titanium is placed in an electrolytic solution and a direct current is passed through the titanium as an anode. 5. The battery according to claim 1, wherein the titanium having an oxide film has a color of pale yellow, golden yellow, blue, or purple.